Sensitizing solid silver halide emulsion layer with hot hydrogen

ABSTRACT

A process is disclosed for increasing the sensitivity of negative-forming radiation sensitive silver halide layers by treating the silver halide layers with hot hydrogen. The layer(s) thus treated exhibit reduced low intensity reciprocity law failure as well as increased sensitivity to electromagnetic radiation. In a preferred embodiment, the treated silver halide layer(s) exhibit practically no low intensity reciprocity law failure.

United States Patent [191 Janusonis SENSITIZING SOLID SILVER HALIDE EMULSION LAYER WITH HOT HYDROGEN [75] Inventor: Gaile A. Janusonis, Rochester, N.Y.

[73] Assignee: Eastman Kodak Company,

Rochester, NY.

OTHER PUBLICATIONS Shin-Flaw Journal of the Optical Society of America", Vol. 34, May, 1944, pgs. 285-289. Response of Type lIIa-j Kodak Spectroscopic Plates to baking in Various Controlled Atmospheres" by A.

[ June 24, 1975 G. Smith, et al., Applied Optics, Vol. 10, July, l97l, pgs. l,597-l599.

Some Effects of Environment on Latent Image Formation by Light" by T. H. James, Photographic Science and Engineering, Vol. 14, No. l, January-February, 1970, pgs. 84-96.

Primary Examiner-Won l-l. Louie, Jr. Attorney, Agent, or Firm-J. T. Lewis ABSTRACT A process is disclosed for increasing the sensitivity of negative-forming radiation sensitive silver halide layers by treating the silver halide layers with hot hydrogen. The layer(s) thus treated exhibit reduced low intensity reciprocity law failure as well as increased sensitivity to electromagnetic radiation. ln a preferred embodiment, the treated silver halide layer(s) exhibit practically no low intensity reciprocity law failure.

6 Claims, No Drawings SENSITIZING SOLID SILVER HALIDE EMULSION LAYER WITH HOT HYDROGEN BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to photography. In one aspect. the invention relates to a process for increasing the sensitivity of photosensitive silver halide layers especially negative forming silver halide emulsion layers and es pecially negative-forming silver halide emulsions layers coated on a support. Products obtained in accordance with the process disclosed herein manifest increased photographic speed and reduced or practically no low intensity reciprocity law failure.

2. Description of the Prior Art Various techniques have been disclosed for increasing the speed of silver halide emulsions which are employed in photographic applications. It is well known, for example. that gelatino photographic silver halide emulsions can be sensitized chemically with a variety of chemical sensitizers. Illustrative of the chemical sensitizers which have been employed are labile sulfur compounds, selenium and tellurium compounds, certain noble metals. so-called reduction sensitizers, or combinations of chemical sensitizers. The chemical sensitizers are described, for example. in U.S. Pat. Nos. 1,623,499 of Sheppard et a1, issued Apr. 5, 1927; 2,399,083 of Waller et a1, issued Apr. 29, 1946; 3,297,446 of Dunn, issued Jan. 10, 1967 and 3,442,653 of Dunn, issued May 6, 1969.

Increasing the grain size of silver halides has been employed in order to provide silver halide materials which evidenced increased sensitivity. The application of vacuum treatment for photographic elements has also been employed in order to increase the speed of photographic materials. Vacuum treatment is described in Belgium Pat. No. 734,571 issued Aug. 14, 1969. 1n accordance with the Belgium patent, degassing a photographic silver halide emulsion through use of a high vacuum, such as, for example, pressures of about torr and exposing the photographic materials in the substantial absence of oxygen and moisture results in some increase in photographic sensitivity of the photographic materials.

The use of pneumatic pressure has been employed as a technique for increasing photographic sensitivity. Journal of the Optical Society of America, Vol. 34, I944, pages 285-289. Influence of Pneumatic Pressure on the Photographic Sensitivity" by Choong Shin- Piaw a technique is described whereby photosensitive silver halide emulsion layers are subjected to pneumatic pressure prior to exposure of such layers to actinic radiation. This reference teaches the use of pneumatic pressure applied by hydrogen, nitrogen or carbon dioxide. The increase in sensitivities as described by Choong are at the most minimal.

lt is also known from U.S. Pat. No. 3,542,557 of I11- ingsworth et al that the sensitivity of silver halide emulsions can be increased if the liquid, bulk emulsions are subjected to pneumatic pressure prior to such emulsions being coated-out onto supporting surfaces. 111- ingsworth et al teach that the pneumatic pressure may be supplied by the use of a wide variety of gases. including nitrogen, carbon dioxide and hydrogen, as well as inert gases such as neon, helium, argon, krypton and xenon.

While the processes described above have succeeded in enhancing the sensitivity, and hence increasing the speed of, photosensitive silver halide emulsion layers, they have not succeeded in increasing the speed to the highly unexpected extent described herein. Moreover, such processes have not been successful in eliminating the problem of reciprocity law failure particularly at very low light intensities, such as those, for example, encountered in the field of astronomy, where it is often desired to photograph under ambient conditions very faintly luminous objects which are far from our planet.

ln U.S. patent application Ser. No. 174,508, filed Aug. 24, 1971, a method is described for accomplishing not only a substantial, unexpected increase in the sensitivity of photosensitive silver halide layers (thereby increasing the speed of such silver halide layers), but also reduction or substantial elimination of low intensity reciprocity failure. That method comprises basically at least two steps; namely:

a. removing from the atmosphere adjacent a solid photographic silver halide layer at least a major portion of atmospheric oxygen and moisture (for example, by subjecting the layer to a relatively high vacuum or by sweeping the atmosphere surrounding the layer with an inert gas), and

b. subsequently contacting the resulting prepared layer with an atmosphere containing hydrogen for a period of time sufiicient to increase the sensitivity of the layer to the desired extent. Whereas the invention of said U.S. application Ser. No. 174,508 represents a very valuable and significant contribution to the art, it nevertheless does require a twostep treatment of photographic elements that contain the solid photosensitive silver halide layers. It remains a desirable objective, however, to simplify the process of hydrogen sensitization" described heretofore in said U.S. patent application Ser. No. 174,508.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved method for hydrogen sensitizing solid photosensitive, negative-forming silver halidecontaining layers in a shorter period of time, and to thereby obtain negative-forming photographic elements which exhibit not only increased sensitivity and speed but also substantially reduced low intensity reciprocity law failure.

it is another object to eliminate the apparent necessity to utilize step (a) as set out above (relating to the description of the processes disclosed in U.S. application Ser. No. 174,508) in processes for the hydrogen sensitization of solid photosensitive silver halide layers.

These objects, as well as others which will be readily apparent from the following description and claims. can be achieved by carrying out the contacting step via the use of relatively hot hydrogen gas (e.g., using hydrogen gas having a temperature of at least about 35C) for a period of time sufficient to obtain the desired degree of sensitization, i.e. preferably for at least about 5 seconds, with time of sensitization being inversely related to the temperature to obtain the desired results.

DESCRIPTION OF A PREFERRED EMBODIMENT In one embodiment of, the present invention, a radiation sensitive negative-forming photographic element comprising at least one negative forming silver halidecontaining layer coated and dried conventionally on a photographic film support (said silver halide layer being a photographic emulsion layer comprising said silver halide dispersed in a water-permeable hydrophilic colloid such as, for example, gelatin) is simply contacted (in an appropriate piece of equipment) for at least about 3 seconds, and preferably for at least about 30 seconds with a stream of hot hydrogen gas (having a temperature 3 35C., preferably at least about 60C and still further preferably about 80C., up to just below the melting point of the continuous phase material in the layer).

DETAILS As employed in this specification, as well as in the ap pended claims, the use of the term atmosphere" is intended to include the mass of air which generally surrounds a radiation sensitive silver salt emulsion layer (some of which atmosphere is usually contained in said layer). Radiation is intended to include any of the known rays such as for example, X-rays, ultraviolet radiation, infrared radiation, actinic radiation as well as electron beams and the like. The term layer is intended to include a silver salt emulsion coated (and dried to a conventional extent) on a film support, a selfsupporting silver salt emulsion, and the like. Preferably the silver salt layer is coated on a support. By negative forming" is meant those photographic elements or layers which can be developed out conventionally to form negative images, the density of which increases with increasing illuminance or with increasing exposure.

Generally, in the practice of the present invention, the relatively hot gas (in the hydrogen contacting step) which is brought into actual contact with the photographic element which is to be hydrogen sensitized" thereby should contain at least about 2 volume percent of hydrogen and can contain as much as 100 volume percent of hydrogen if desired Any remaining portion of the hot gas should be a non-reactive gas (such as, for example, nitrogen, argon, neon, helium, and the like), although a small amount (preferably below about 5 volume percent) of moisture vapor and/or oxygen can sometimes be tolerated in the hot contacting gas (keeping in mind that mixtures of hydrogen and oxygen gases are usually extremely dangerous due to their extreme explosive potential). Hereinafter, where the term hydrogen" is utilized (unless specific otherwise) in the description portion of this disclosure (but not in the examples), it should be kept in mind that mixtures of H with one or more non-reactive gases can be used. Actually, if will be appreciated that different photographic products react somewhat differently to any specified condition of temperature, time and pressure depending upon the various ways in which they were manufactured and the various addenda they contain. However, when one desires relatively quick hydrogen sensitization, relatively hotter contacting gas (up to about lC, for example, or higher if desired) and/or relatively higher concentrations of hydrogen in the hot contacting gas should be utilized. For example, substantially dry contacting gas consisting essentially of from about 20 to about 80 volume percent of hydrogen and from about 80 to about 20 volume percent of nitrogen and having a temperature of from about 65 to about 80C represent materials for use in a particularly preferred embodiment of the present invention. It has been observed that mixtures of hydrogen with inert gas(es) function in very 1:.ucli the same manner as does pure hydrogen gas at a corresponding reduced pressure (eg, 25 percent hydrogen or one-fourth atmosphere, respectively). Since it is the temperature of the hydrogen when it is in contact with the emulsion layer which is important, for the successful practice of this invention the hot hydrogen" temperatures herein can be obtained by using a heated emulsion layer, even though the mass of gas in the atmosphere around or over the emulsion may be relatively cool. The emulsion can be heated by contact with a hot drum either prior to or during the contact with hydrogen.

Although the prior art references noted above describe the use of a variety of gases for the purpose of applying pneumatic pressure to liquid, undried silver halide emulsions, or to silver halide emulsion layers, before exposures to actinic radiation, it has been found that the enhanced results which are achieved in accordance with this invention are only obtained with the use of hydrogen gas. The use of other gases, such as for example, nitrogen or carbon dioxide, or inert gases such as neon, helium, argon, krypton or xenon (in the absence of hydrogen), fail to provide the enhanced results otherwise achieved in accordance with the process of this invention. it is particularly noteworthy that whereas the prior art is especially concerned with pneumatic pressure as applied to photographic elements, in accordance with this invention the concern is with the treatment of radiation sensitive silver salt layers with hydrogen irrespective of the pressure.

The time during which the hot hydrogen treatment of the present invention is maintained can vary widely depending on several factors such as the particular radiation sensitive materials being sensitized, the presence or absence of sensitizing dyes or chemical sensitizers, the actual temperature of the hot hydrogen treatment, the pressure of the hydrogen atmosphere, the desired degree of sensitivity, and the like. Typically, the treatment can be maintained from a fraction of a second to about 24 hours or more. In accordance with a preferred embodiment of the invention the hot hydrogen atmosphere is maintained in contact with the element from about 3 seconds to about 24 hours. In accordance with another embodiment of the invention the hot hydrogen treatment is maintained from about 1 minute to about 2 hours.

A wide variation in pressures can be suitably employed during the treatment of the radiation sensitive silver layers with hot hydrogen. The pressure can range from as low as l0 torr up to about l00 atmospheres. Preferably the hot hydrogen treatment is performed at a pressure of from about 0.5 to about l0 atmospheres. In accordance with the most preferred aspect the hot hydrogen treatment is performed at from about 0.8 to about 1 atmosphere. Although an increase in sensitivity is obtained in all cases upon treatment of stabilized radiation sensitive elements with hot hydrogen as set out above, a decrease in the optimum effects is sometimes obtained at very high pressures such as about above I00 atmospheres.

The practice of the present invention can result in the production of radiation sensitive silver halide layers having a substantially constant density when exposed to the same quanta of radiation over a range of from about 10 or lower to about 10 seconds and developed. These layers can be produced in accordance with the processes described above. As a basis for a test, for example. of this property any reasonable developed density can be used. It is preferred, however. that a developed density of about 0.4 above fog be utilized. The use of still lower developed densities can be used for this test in order to more stringently demonstrate the resistance or immunity to low level reciprocity failure property of these photographic elements. In accordance with a preferred aspect of the invention the radiation sensitive silver halide layers which are treated thereby comprise at least one gelatino silver halide emulsion layer on a photographic film support. The radiation sensitive emulsions can be chemically sensitized and/or spectrally sensitized. In a preferred embodiment the radiation sensitive emulsions are chemically and spectrally sensitized.

The process of this invention can be employed for increasing the sensitivity and for reducing the low intensity reciprocity law failure for a variety of radiation sensitive silver salt layers. The radiation sensitive material can be non-spectrally sensitized, such as X-ray emulsions, electron and particulate recording materials, or emulsions which are orthochromatic, panchromatic, infrared-sensitive and the like containing spectral sensitizing dyes. The photographic silver halide emulsion layers which are treated in accordance with this invention may contain a variety of photographic addenda, including for example, speed increasing compounds, stabilizing compounds or antifogging compounds.

The process of this invention is particularly useful for treating photosensitive silver halide emulsion layers wherein very little or no low intensity reciprocity law failure is tolerable. This is applicable, for example, for photographic plates or films for recording images with radiation of so-called short wavelengths, e.g., wavelengths of less than about 400 to 500 nm, for visible radiation, e.g., wavelengths of about 400 to 700 nm or for wavelengths of above about 800 nm in which long exposure times are employed, such as several seconds to several hours or longer. It is also particularly advantageous to treat high speed films in accordance with this invention. especially those films having a log speed greater than about 200. The log speed, as employed herein, equals I l-log E) when the time of exposure is 1/25 of a second and E is the exposure measured in meter-candle-seconds necessary to produce a density of 0.3 above fog when the photographic material is processed for 4 minutes at 21C in Kodak Developer D-I 9 diluted 1:1 by volume with water. Kodak Developer D-l9 has the following composition:

water (about 50C) N-methyl-p-aminophenol sulfate sodium sulfite. desiccated 38 hydroquinone sodium carbonate, desiccated potassium bromide water to make The described photosensitive materials employed in the practice of the invention contain a photosensitive silver salt, especially a photographic silver salt. Suitable photographic silver salts include silver chloride, silver bromide, silver bromoiodide, silver iodobromide, silver iodochloride, silver chloroiodide, silver chlorobromoiodide or mixtures thereof. The photographic silver halide can be coarse or fine-grain and the emulsion containing the photographic silver halide can be prepared by any of the well-known procedures in the photographic art, such as single-jet emulsions, double-jet emulsions, Lippmann emulsions, ammoniacal emulsions, thiocyanate or thioether ripened emulsions, such as those described in the U.S. Pat. Nos. 2,222,264 of Nietz et al issued Nov. I4, I940; 3,320,069 of lllingsworth issued May 15, I967 and 3,271,157 of McBride issued Sept. 6, 1966. Surface image silver halide emulsions can be used or internal image silver halide emulsions such as those described in U.S. Pat. Nos. 2,592,250 of Davey et al issued Apr. 8, 1952 and 3,206,313 of Porter et al issued Sept. 14, I965. If desired, mixtures of surface and internal image silver halide emulsions can be used as described in U.S. Pat. No. 2,996,382 of Luckey et al issued Apr. 15, I96]. The silver halide emulsion can be a regular grain emulsion such as cubic or octahedral silver halide crystals having a single morphology, as described in Klein and Moisar, Journal of Photographic Science, Volume 12. No. 5, September-October 1964, pages 242-25I.

The silver halide emulsion employed in the practice of the invention can be unwashed or washed to remove soluble salts. In the latter case the soluble salts can be removed by chill setting and leaching or the emulsion can be coagulation washed.

The silver halide employed in the practice of the invention can be sensitized with chemical sensitizers, such as with reducing agents; sulfur, selenium, or tellurium compounds; gold, platinum or palladium compounds, or combinations of these. Suitable procedures are described, for example, in U.S. Pat. Nos. 1,623,499 of Sheppard issued Apr. 5, I927; 2,399,083 of Waller et al issued Apr. 23, I946; 3,297,447 of McVeigh issued .Ian. 10, 1967 and 3,297,446 of Dunn issued Jan. I0, 1967.

The silver halide emulsions used with this invention can contain speed increasing compounds, such as those described in Paragraph IV; antifoggants and stabilizers such as those described in Paragraph V; incorporated developing agents such as those described in Paragraph VI; hardeners such as those described in Paragraph Vll; all at pages I07 and 108 of the Product Licensing lndex, Vol. 92, December, 1971.

A photographic element or emulsion described and used in the practice of the invention can contain various colloids alone or in combination as vehicles, binding agents and in various layers. They are transparent or translucent and include both naturally-occurring substances such as proteins, for example, gelatin, gelatin derivatives, cellulose derivatives, polysaccharides such as dextran, gum arabic and the like; and synthetic polymeric substances such as water-soluble polyvinyl compounds like poly(vinyl pyrrolidone), acrylamide polymers and the like. Other synthetic polymeric compounds which can be employed include polyvinyl butyral, ethyl cellulose, polyvinylidene chloride, dispersed vinyl compounds such as in latex form and particularly those which increase dimensional stability of photographic materials. Suitable synthetic polymers include those described in U.S. Pat. Nos. 3,142,586 of Nottorf issued July 28, I964; 3,l 93,386 of White issued July 6, 1965; 3,062,674 of Houck et al issued Nov. 6, 1962; 3,220,844 of l-louck et al issued Nov. 30, 1965; 3,287,289 of Ream et al issued Nov. 22, I966 and 3,41 1,911 of Dykstra issued Nov. 19, 1968. Effective polymers include water insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates, and those which have crosslinking sites which facilitate hardening and curing as well as those having recurring sulfobetaine units as described in Canadian Pat. No. 774,054. Binderless photosensitive silver compounds can be employed, such as described in British Pat. Nos. 1,134,007 and 977.291.

The photographic and other layers of an element employed in the practice of the invention and described herein can be coated on a wide variety of supports. Typical supports include cellulose nitrate film, cellulose ester film. poly (vinylacetal) film, polystyrene film. poly(ethylene terephthalate) film, polycarbonate film and related films or resinous materials, as well as glass, paper, metal and the like. In the case of a paper support, it can be partially acetylated or coated with baryta and/or an alpha olefin polymer, particularly a polymer of an alpha olefin containing 2 to 10 carbon atoms such as polyethylene, polypropylene, ethylene-butene copolymers and the like.

The photographic elements or layers employed in the practice of this invention can contain antistatic or conducting layers such as those described in Paragraph 1X; plasticizers and lubricants such as those described in Paragraph X1; surfactants such as those described in Paragraph Xll; matting agents such as those described in Paragraph Xlll', brightening agents or scintillating agents such as those described in Paragraph XIV; light absorbing or light scattering materials such as those described in Paragraph XVI; and spectral sensitizing dyes such as those described in Paragraph XV; all at pages 108 and 109 of the Product Licensing Index, Volume 92, December, 1971.

The photographic layers used in the practice of the invention can be coated by various coating procedures including dip coating, airknife coating, curtain coating or extrusion coating using hoppers such as described in U.S. Pat. No. 2,681,294 of Beguin issued June 15, 1954. If desired, two or more layers can be coated simultaneously such as by the procedures described in U.S. Pat. No. 2,761 ,791 of Russell issued Sept. 4, 1956 and British Pat. No. 837,095.

The sensitizing dyes and other addenda used in the practice of the invention can be added from water solutions or suitable organic solvent solutions can be used. The compounds can be added using various procedures including, for example, those described in U.S. Pat. Nos. 2,912,343 of Collins et a1 issued Nov. 10, 1959; 3,342,605 of McCrossen et a1 issued Sept. 19, 1967; 2,996,287 of Audran issued Aug. 15, 1961 and 3,425,835 of Johnson et a1 issued Feb. 4, 1969.

As described, the process can be employed for treatment of other photographic elements also, such as those described in U.S. Pat. Nos. 2,756,227 of Heseltine, issued July 24, 1956 and 2,734,900 of Heseltine, issued Feb. 14, 1956. The invention can be employed for preparing elements designed for colloid transfer processes, such as described in U.S. Pat. No. 2,716,059 of Yutzy et al, issued Aug. 23, 1955, silver salt diffusion transfer processes, such as described in U.S. Pat. Nos. 2,352,014 of Rott, issued June 20, 1944; 2,543,181 of Land, issued Feb. 27, 1951; 3,020,155 of Yackel et al, issued Feb. 6, 1962; and 2,861,885 of Land, issued Nov. 25, 1958; as well as elements designed for color image transfer processes, such as described in U.S. Pat. Nos. 3,087,817 of Rogers, issued Apr. 30, 1963; 3,185,567 of Rogers, issued May 25, 1965; and 2,983,606 of Rogers, issued May 9, 1961; and photographic elements employed for imbibition transfer processes, such as described in U.S. Pat. No. 2,882,156 of Minsk, issued Apr. 14, 1959.

The process can be employed for treating elements designed for physical development, such as described in British Pat. Nos. 920,277 published Mar. 6, 1963; and 1,131,238 published Oct. 23, 1968.

The process of this invention can also be employed for treatment of elements designed for color photography such as those described in Paragraph XXll on page of Product Licensing Index, Volume 92, December, 1971.

Photographic elements prepared according to the invention can be processed by various methods, after exposure, including processing in silver halide developer solutions containing various silver halide developing agents. such as alkaline solutions containing such silver halide developing agents as hydroquinones, catechols, aminophenols, 3-pyrazolidones, ascorbic acid and ascorbic acid derivatives, hydroxylamines, hydrazines, reductones, and the like. The elements can be processed by so-called web processing, such as described in U.S. Pat. No. 3,179,517 of Tregillus et a1 issued Apr. 20. 1965; stabilization processing; such as described in Russell et al, Stabilization Processing of Films and Papers, P.S.A. Journal Vol. 16B, August, 1950; monobath processing, such as described in The Monobath Manual," by Grant M. Haist, 1966 and U.S. Pat. No. 3,392,019 of Barnes et al issued July 9, 1968. if desired, photographic elements prepared according to the invention can be processed in hardening developers, such as described in U.S. Pat. No. 3,232,761 of Allen et a1 issued July 24, 1962. It also includes, for example, elements designed to be developed in solutions containing color-forming couplers, such as described in U.S. Pat. Nos. 2,252,718 of Mannes et :11 issued Aug. 19, 1941; 2,592,243 ofCarroll et a1 issued Apr. 8, 1952 and 2,950,970 of Schwan et al issued Aug. 30, 1960. The process can also be employed for treatment of socalled false-sensitized color materials, such as those described in U.S. Pat. No. 2,763,549 of Hanson issued Sept. 18, 1956.

The process of the invention can be used for treat rnent of photosensitive silver halide layers used for providing high contrast images, such as employed in the graphic arts. These can be so'called lith emulsions. Also the silver halide emulsion containing elements of this invention, on an appropriate substrate and appropriately sensitized, can be employed for making lithographic printing plates.

As described herein, this invention is advantageously employed in combination with photographic systems adapted for dry process. Stabilized print out elements are typical of the silver halide photographic elements adapted for dry process.

Typical of photographic layers capable of being dry processed and which are advantageously treated in accordance with this invention are the so-called photosensitive elements", (i.e., a latent image is formed imagewise in the exposed areas of a silver salt layer) and thermosensitive elements" (i.e., substantially permanent visible images of photographic sharpness and high visual contrast can be produced within seconds through the mere application of heat).

Typically a dry photographic" element comprises a support having thereon an oxidation-reduction image forming combination said combination comprising a silver salt. preferably an organic silver salt, and a reducing agent. and a catalyst for the oxidation-reduction image forming combination. Typical dry photographic products are described in US. Pat. Nos. 3,392,020 of Yutzy et al issued July 9, 1969, 3,667,958 of Evans entitled Photosensitive and Thermosensitive Elements, Compositions and Processes" in 3,672,904 of deMauriac entitled Element, Composition and Process" and in co-pending US application Ser. No. 70,466 of deMauriac and Gaugh, entitled Element, Composition and Process" filed Sept. 8, l970.

Any of the typical reducing agents can be employed in combination with the oxidation portion of the image forming system, such as for example, the prior art silver halide reducing agents as described in said deMauriac, US. Pat. No. 3,672,904.

As the oxidizing agent, of the oxidizing-reduction image forming combination, a silver salt of an organic acid is preferably employed. The silver salt of an organic acid should be resistant to darkening under illumination to prevent undesired deterioration of a developed image. An especially suitable class of silver salts of organic acids is the water insoluble silver salts of long-chain fatty acids which are stable to light. Typically, the silver salts include silver behenate, silver stearate. silver oleate, silver laurate, silver hydroxystearate, silver caprate, silver myristate, and silver palmitate. Other suitable oxidizing agents are silver benzoate, silver phthalazinone, silver benzotriazole, silver saccharin, silver 4'-n-octadecyloxydiphenyl-4-carboxylic acid, silver orthoaminobenzoate, silver acetamidobenzoate, silver furoate, silver camphorate, silver pphenylbenzoate. silver phenyl acetate, silver salicylate. silver butyrate, silver terephthalate, silver phthalate, silver acetate, and silver acid phthalate. Non-silver salts can be employed as oxidizing agents, such as zinc oxide, gold stearate. mercuric behenate, auric behenate and the like; however, silver salts are generally preferred.

Typically, a photosensitive silver salt is present in dry photographic elements in minor or catalytic amounts and in catalytic proximity to the oxidation image forming component of the image forming combination. A suitable concentration range of the catalyst is generally from about 0.01 to about 0.50 mole of photosensitive silver salt per mole of oxidizing agent. Suitable silver salts include photosensitive silver halides, e.g., silver chloride, silver bromide, silver bromoiodide, silver chlorobromoiodide, or mixtures thereof. The photosensitive silver halide can be coarse or fine-grain, very fine-grain emulsions being especially useful. The emulsion containing the photosensitive silver halide can be prepared any of the well-known procedures in the photographic art such as described above.

The dry photographic elements preferably contain an activator-toning agent. Suitable activator-toning agents which can be employed include cyclic imides such as:

Phthalimide.

N-Hydroxyphthalimide,

N-Potassium phthalimide,

N-Mercury phthalimide,

Succinimide, and

N-Hydroxysuccinimide.

Other activator-toning agents can be employed in combination with or in place of the cyclic imides. Such other activator-toning agents are generally heterocyclic compounds containing at least two hetero atoms in the heterocyclic ring at least one being nitrogen. Illustrative compounds include phthalazinone, phthalic anhydride, 2-acetylphthalazinone and 2- phthalylphthalazinone. Grant, US. Pat. No. 3,080,254 issued Mar. 5, 1963. and Workman US. Pat. No. 3,446,648 issued May 27, I969, described suitable activator-toning agents.

Activator-toning agents are suitably employed at a concentration of about 0.10 to about l.05 moles per mole of oxidizing agent, however, lower and higher concentrations can be employed.

The exact mechanism by which the process of the invention provides increased sensitivity and reduced to no low intensity reciprocity law failure as evidenced by the substantially constant density obtained by negativeforming radiation sensitive materials when exposed to the same quanta of radiation over a very broad range of exposure time and developed is not fully understood. However, as demonstrated herein, surprisingly increased sensitivity and reduced reciprocity law failure is provided according to the invention. For example, recording film containing a photographic silver halide emulsion which is chemically sensitized to a high speed can be further sensitized according to the invention.

The following examples are included for a further understanding of the invention.

In the following Example I, a comparison is presented between the 2-step process described in said US. application Ser. No. 174,508, filed Aug. 24, 1971, and the present improved process.

EXAMPLE I a. Control As a control, a photographic element is prepared by coating and drying conventionally an aqueous photographic (0.25p.m) silver bromide emulsion (which is non-chemically sensitized) at a level of 10.76 mg. silver/dm and 21.52 mg. gelatin/dm on a polyethylene terephthalate film support. This emulsion contains no spectral sensitizing dyes.

Samples of the above film were placed into an apparatus designed so that the atmosphere in that part of the apparatus in which the film was placed could be substantially removed (by evacuation, for example) or replaced (by sweeping with another gas, for example). Tests were made at several different temperatures, as set out in Table l below. In each instance, for purposes of comparison, the apparatus was first evacuated for 30 minutes (to about 0.1 torr) and then subjected to one atmosphere of hydrogen gas for 20 minutes. Following the hydrogen sensitization step, the apparatus was flushed with N gas. The resulting film samples were then removed from the container, exposed for l0 seconds before a xenon flash and processed for 6 minutes in Eastman Kodak Developer DK-50. Sensitometric results from there tests are also shown in Table l, below (under the sub-heading control).

b. The Present Invention The procedure for the control samples," above was repeated. except that in these experiments the films were not subjected to a vacuum pretreatment step. instead, the films were simply treated, at the various temperature, by flowing hydrogen gas through the apparatus (at about 1 atmosphere of pressure) for about 15 seconds, and then holding the samples in hydrogen gas at about 1 atmosphere pressure during the hydrogen sensitization period. Sensitometric data for these tests also appear in Table l, below, under the sub-heading This Invention."

measured at 0.30 above D These results illustrate particularly the advantage of using the present invention at treatment temperatures above about 35C., i.e., a vacuum pretreatment step is not necessary.

EXAMPLE 2 Several photographic elements were manufactured by coating and drying a conventional sulfur and gold sensitized, silver chlorobromide gelatin emulsion onto a cellulose acetate film support. The emulsion was one that had had its natural sensitivity extended to 710 nm. by the presence of a conventional sensitizing dye selected for its ability to accomplish such extended sensitization. The resulting elements were treated, with only a 30 second initial evacuation step (as a safety precaution) at about I torr, with hydrogen gas in the apparatus of Example I at various temperatures and at various times, as set out in Table ll, below. Exposure was for l seconds to a xenon flash. Development was for 8 minutes at C. in Eastman Kodak Developer D-l9. This evacuation is not necessary in the commercial practice of the present invention.

measured at 0.30 above Dmln.

These elements also display similar excellent resistance to low level reciprocity failure, as compared with elements made via the process of said US. application Ser. No. [74,508.

It is believed that similar excellent hydrogen sensitization" can be accomplished via the present improved process with any of the negative-forming silver halidecontaining photographic elements referred to hereinbefore, whether they be monolayer or multilayer, color or black and white. Details of various aspects of development, element manufacture and experimental treatment of the resulting elements (including measurement of the elements for resistance to low level reciprocity failure) can be found in said US. application Ser. No. l74,508, filed Aug. 24, 1971. However, such details are well known to the ordinarily skilled artisan in the photographic art and do not constitute an essential part of the present invention and therefore need not be repeated here.

One other aspect of the present invention relates to a novel property of the hydrogen sensitized elements that result from practicing the present sensitizing processes. Thus, it has been discovered that, contrary to what would ordinarily be expected, the sensitivity of hydrogen sensitized elements, for some as yet unexplainable reason. increase still further when the elements are stored for an extended period of time under ambient conditions before being developed, but after imagewise exposure of the elements. This storage after exposure" aspect of the present invention is illustrated in the following Example 3.

EXAMPLE 3 a. (Control-no storage) A photographic element was prepared having a dried layer of conventionally sulfur and gold sensitized silver chlorobromide gelatin emulsion featuring extended sensitization to 710 nm. A sample of this element was exposed for IO" seconds to a xenon arc in room air and then developed for 8 minutes in Eastman Kodak Developer D-l9. Sensitometric data for the developed film is given in Table II], below, under the designation $LA.\7

b. (H; sensitized-no storage) A sample of the element described in paragraph a of this Example 3 was hydrogen sensitized by a process like that of Example 2, above. with a vacuum pretreatment for about 1 hour and at about 23C. It was then exposed and developed as in paragraph a of this Example 3. Sensitometric data for the developed film is given in Table 1]], below, under the designation B.

c. (H sensitized-storage before exposure) Paragraph b of this Example 3 above, was repeated, except that the sample element was stored for l month under ambient conditions (room air) before the exposure and development thereof. Sensitometric data for the developed film is given in Table lll, below, under the designation C."

d. (H Sensitization-storage after exposure but before development) e. (Control-storage after exposure) Paragraph a of this Example 3, above, was repeated except that the sample element was stored under ambient conditions (room air) for one month after exposure, but before being developed. Sensitometric data for the developed film is given in Table III, below, under the designation E."

Table I" Relative Sample Speed 1! D... mw

A )0 2.23 0.06 2.54 B l4l L96 0.10 2.56 C 123 2.28 0.16 2.58

Table Ill-Continued Relative Sample Speed 1/ DWI" u"...

D 2l4 2.l5 0.12 2.56 E 97 2.34 0.08 2.58

measured at 0.] above Dunn Generally, beneficial results from such a special expose-store-develop procedure can be obtained when such storage (between exposure and development of the element) is accomplished in a few seconds, and preferably for at least about 24 hours to 5 days or more at a temperature offrom about [5 to about 120C. The temperature of storage is inversely proportional to time of storage for equivalent beneficial results. The storage can be carried out in room-air or in an inert atmosphere, e.g.. nitrogen.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

What is claimed is:

l. A process for increasing the sensitivity of a solid radiation-sensitive negative-forming layer containing at least one radiation-sensitive silver halide, which process comprises the step of contacting said layer with a gaseous atmosphere containing at least about 2 volume percent of hydrogen and at most about 5 volume percent moisture at a temperature of at least about 35C. and for at least about 5 seconds until the sensitivity of said layer is increased; said process being performed without subjecting said layer to an evacuation step prior to said contacting with hydrogen; any other gases in said contacting gaseous atmosphere being nonreactive with said layer.

2. A process as in claim 1, wherein said silver halide is suspended in said layer in a hydrophilic colloid matrix.

3. A process as in claim 2, wherein said temperature is from about 60 to about C, and below the melting point of said hydrophilic colloid matrix.

4. A process as in claim 2, wherein said contacting gaseous atmosphere contains a mixture of hydrogen and at least one non-reactive gas.

5. A process as in claim 4, wherein said non-reactive gas is nitrogen.

6. A process as in claim 3, wherein said hydrophilic colloid is gelatin. 

1. A PROCESS FOR INCREASING THE SENSITIVITY OF A SOLID RADIATION-SENSITIVE NEGATIVE-FORMING LAYER CONTAINING AT LEAST ONE RADIATION-SENSITIVE SILVER HALIDE, WHICH PROCESS COMPRISES THE STEP OF CONTACTING SAID LAYER WITH A GASEOUS ATMOSPHERE CONTAINING AT LEAST ABOUT 2 VOLUME PERCENT MOISTURE AT A TEMPERATURE MOST ABOUT 5 VOLUME PERCENT MOISTURE AT A TEMPERATURE AT LEAST ABOUT 35*C. AND FOR AT LEAST ABOUT 5 SECONDS UNTIL THE SENSITIVITY OF SAID LAYER IS INCREASED; SAID PROCESS BEING PERFORMED WITHOUT SUBJECTING SAID LAYER TIO AN EVACUATION STEP PRIOR TO SAID CONTACTING WITH HYDROGEN; ANY OTHER GASES IN SAID CONTACTING GASEOUS ATMOSPHERE BEING NON-RECTIVE WITH SAID LAYER.
 2. A process as in claim 1, wherein said silver halide is suspended in said layer in a hydrophilic colloid matrix.
 3. A process as in claim 2, wherein said temperature is from about 60* to about 120*C., and below the melting point of said hydrophilic colloid matrix.
 4. A process as in claim 2, wherein said contacting gaseous atmosphere contains a mixture of hydrogen and at least one non-reactive gas.
 5. A process as in claim 4, wherein said non-reactive gas is nitrogen.
 6. A process as in claim 3, wherein said hydrophilic colloid is gelatin. 